1. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 1 Security Systems Lecture notes Dr. Clifford Neuman University of Southern California Information Sciences Institute

2. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 2 CSci530: Security Systems Lecture 5 – September 24, 2004 Key Management (2) Dr. Clifford Neuman University of Southern California Information Sciences Institute Slides by Drs. Brian Tung and Clifford Neuman

3. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 3 Administration v Assignment 1 is on web page –Due October 1 –Corrections posted last night (typos) v Paper proposal assignment on web –Proposals due October 8 –Will respond sooner if received early –Be sure to send queries to correct address

4. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 4 Key Management v Key management is where much security weakness lies –Choosing keys –Storing keys –Communicating keys

5. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 5 Key Management Review v Classes of Crypto –Public key – 2n keys –Conventional n 2 keys

6. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 6 Public Key Distribution v Public key can be public! –How does either side know who and what the key is for? Private agreement? (Not scalable.) v Does this solve the key distribution problem? –No – while confidentiality is not required, integrity is.

7. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 7 Certification Infrastructures v Public keys represented by certificates v Certificates signed by other certificates –User delegates trust to trusted certifiers. –Certificate chains transfer trust several steps

8. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 8 Examples v PGP –“Web of Trust” –Can model as connected digraph of signers v X.500 –Hierarchical model: tree (or DAG?) –(But X.509 certificates use ASN.1!)

9. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 9 Examples v SSH –User keys out of band exchange. –Weak assurance of server keys. u Was the same host you spoke with last time. –Discussion of benefits v SET –Hierarchical –Multiple roots –Key splitting

10. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 10 What to do with keys v Practical issues –How to carry them u Passwords vs. disks vs. smartcards –Where do they stay, where do they go –How many do you have –How do you get them to begin with.

11. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 11 Key Distribution v Conventional cryptography –Single key shared by both parties v Public Key cryptography –Public key published to the world –Private key known only by owner v Third party certifies or distributes keys –Certification infrastructure –Authentication

12. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 12 Practical use of keys v Email (PEM or S/MIME) –Hashes and message keys to be distributed and signed. v Conferencing –Group key management (discussed later) v Authentication (next lecture) v SSL –And other “real time” protocols –Key establishment

13. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 13 Recovery from exposed keys v Revocation lists (CRL’s) –Long lists –Hard to propogate v Lifetime / Expiration –Short life allows assurance of validitiy at time of issue. v Realtime validation –Online Certificate Status Protocol (OCSP) v What about existing messages?

14. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 14 Key Management Overview v Key size vs. data size –Affects security and usability v Reuse of keys –Multiple users, multiple messages v Initial exchange –The bootstrap/registration problem –Confidentiality vs. authentication

15. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 15 Key Management Review v KDC’s –Generate and distribute keys –Bind names to shared keys

16. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 16 Key Management Overview v Who needs strong secrets anyway –Users? –Servers? –The Security System? –Software? –End Systems? v Secret vs. Public

17. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 17 Security Architectures v DSSA –Delegation is the important issue u Workstation can act as user u Software can act as workstation –if given key u Software can act as developer –if checksum validated –Complete chain needed to assume authority –Roles provide limits on authority – new sub-principal

18. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 18 Group Key Management v Group key vs. Individual key –Identifies member of groups vs. which member of group –PK slower but allows multiple verification of individuals

19. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 19 Group Key Management Issues v Revoking access –Change messages, keys, redistribute v Joining and leaving groups –Does one see old message on join –How to revoke access v Performance issues –Hierarchy to reduce number of envelopes for very large systems –Hot research topic

20. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 20 Group Key Management Approaches v Centralized –Single entity issues keys –Optimization to reduce traffic for large groups –May utilize application specific knowledges v Decentralized –Employs sub managers v Distributed –Members do key generation –May involve group contributions

21. Copyright © 2003-2004 B. C. Neuman, - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Fall 2003 21 Current event Slashdot (by CmdrTaco Tuesday September 14, @03:24PM)CmdrTaco Saint Aardvark writes "Lexar describes the JumpDrive Secure as "loaded with software that lets you password- protect your data. If lost or stolen, you can rest assured that what you've saved there remains there with 256-bit AES encryption." @stake has a different take: The password can be observed in memory or read directly from the device, without evidence of tampering." And best of all, the punch line: "[The password] is stored in an XOR encrypted form and can be read directly from the device without any authentication." That's why I use ROT-13 for my encryption needs."Saint AardvarkLexar@stake has a different take